It is common practice in semiconductor integrated circuit technology to interface different transistor technologies in electronic systems and subsystems. It is further common practice to integrate different transistor technologies on the same semiconductor chip. In order to interface the different technologies, it is often necessary to provide voltage level shifting at the interface of the different technologies for proper circuit operation. For example, when interfacing emitter coupled logic (ECL) to metal-oxide field effect transistor (MOSFET) circuits, it may be necessary to shift voltages between 1.5 volts and 15 volts.
Further challenges of interfacing different technologies are presented when it is necessary to interface low voltage circuits to high voltage circuits. A typical example includes low voltage CMOS circuits that may be used in electronic systems for their low power dissipation and high transistor density characteristics, but may be required to drive high voltage circuits as may be found in display driver and automotive applications. The high voltage circuits often have breakdown voltages that are greater than can be tolerated by the low voltage circuits.
In automotive circuits, bipolar and MOS power transistors having high voltage breakdown characteristics are used to drive solenoids and DC motors for such applications as anti-skid braking systems, electric fuel pumps, windshield wipers, power windows and locks, etc. These power transistors, however, are normally controlled and driven by low power, low voltage control circuits. Power field effect transistors such as lateral and vertical DMOS devices are especially useful for driving solenoids and DC motors since the transistors exhibit a very low on resistance and thus have a very small voltage drop across their load terminals. Such power field effect transistors then, are capable of driving solenoids and DC motors very efficiently while being able to withstand high voltages.
In order to reduce the power field effect transistor on-resistance to a minimum, it is necessary to drive the gate voltage above the supply voltage of the power devices. The battery voltage in the automobile, and hence the supply voltage of the power field effect transistor, may vary from approximately 5.5 volts up to 36 volts. Breakdown voltages of present-day power field effect transistors may exceed 80 volts. It would be desirable then, to drive the gate of the power field effect transistor to a level higher than its supply voltage but less than the breakdown voltage of the power field effect transistor. Because low voltage semiconductor circuits have excellent transistor densities and good yield, they are extremely useful as control and driving circuits for high voltage circuit applications when the high voltage interface can be bridged.
Thus, what is needed is a semiconductor voltage level conversion circuit for providing an output voltage that is shifted above both the level of the supply voltage and the breakdown voltage of the semiconductor circuit.